The former All Blacks pivot will face a Rugby Football Union disciplinary hearing in Bristol on Monday night.

And if he is banned - three-week suspensions were handed out for similar offences to Harlequins centre Stuart Abbott and London Irish scrum-half Paul Hodgson earlier this season - then it could be a major blow to Saints' Heineken Cup hopes.

Spencer was yellow-carded by referee Nigel Owens for a tackle on Dragons' Welsh international scrum-half Gareth Cooper at Rodney Parade.

The New Zealander had initially failed to retreat 10 metres following a penalty awarded against Northampton, then he appeared to dump Cooper head-first into the turf.

Cooper was not injured, but Spencer's action threatened to spark a brawl between players from both sides before Owens intervened.

Northampton open their Heineken Cup campaign away to French giants Biarritz on Sunday week, before hosting Borders six days later.

Spencer, though, could now miss both of those Pool Six games, with Saints having already lost captain Bruce Reihana and England hooker Steve Thompson to injuries.

Spencer was reported by independent citing officer Alan Mansell. The three-man RFU panel will be chaired by Christopher Quinlan.

Northampton have already fully assessed the eighth-minute incident during a game when Spencer later limped off suffering from a recurrence of groin trouble.

"We have conducted a full internal investigation into the alleged incident," said Saints rugby director Budge Pountney.